1. Field of the Invention
The present invention relates to pyrolysis or mild gasification of coal and an apparatus suitable for conversion of both caking and non-caking coals. The process and apparatus of this invention provides selectivity of desired products with high yields of aromatic oils and tars and reactive char.
2. Description of the Prior Art
U.S. Pat. No. 4,331,529 teaches a coking and gasification process wherein carbonaceous feed stock, such as hydrocarbon liquids or coals, are introduced to a fluidized bed coking zone producing vapor phase products, including normally liquid hydrocarbons, and coke which is deposited on fluidized solids. The coke and fluidized solids are then passed through a heater to a first fluidized bed gasification zone where a portion of the coke is reacted with an oxygen containing gas to produce gaseous products and partially gasified coke. A portion of the partially gasified hot coke is then passed to a second fluidized bed gasification zone and reacted with steam to produce hydrogen and carbon monoxide. Thermal energy is transferred to the first fluidized bed gasification zone by recirculating a portion of the partially gasified coke deposited on the fluidized bed solids, such as silica or alumina from the second gasification zone.
U.S. Pat. No. 4,721,514 teaches a coal gasification process of injecting raw coal powder with oxygen or air and steam into a fluidized bed reaction chamber and reacting the coal, steam and oxygen under gasification conditions producing gas, char and ash. The '514 patent further teaches agglomerating the ash product produced in the fluidized bed to attain ash with a diameter of between 2.5 mm and 10 mm, causing it to drop from the reaction chamber through a throat against a gas stream into a combustion chamber. The char and injected coal is combusted in the combustion chamber to produce hot fluidizing gas to establish and maintain the fluidized bed gasification conditions in the reaction chamber. The agglomerated ash is fused during combustion and withdrawn from the combustion chamber.
U.S. Pat. No. 3,960,700 teaches adding crushed coal and hot hydrogen into the upper portion of a reactor for rapid heating of the coal. The coal and hot hydrogen reacts at 400.degree. to 2000.degree. C. and at pressures ranging from 500 to 5000 psig followed by rapid quenching so that the total residence time is less than 2 seconds. U.S. Pat. No. 4,012,311 teaches a process for hydropyrolysis of coal requiring at least two serially oriented reaction zones. Coal and hot hydrogen is fed to a first reaction zone at the upper portion of a reactor maintained at a pressure less than 450 psia and a temperature of 400.degree. to 2000.degree. C. with shock quenching with hydrogen below 0.degree. C. and a total residence time less than 2 seconds. Residual carbonaceous material is introduced into a subsequent reaction zone and the same process repeated.
The first two above mentioned patents refer to high pressure hydropyrolysis or staged fluidized bed pyrolysis using air as an oxidant while the last two patents refer to hydropyrolysis processes designed to directly produce high quality, low boiling aromatics, primarily benzene. The byproduct fuel gas and char are used primarily to supply hydrogen and process energy. None of these patents suggest any processes or apparatus having the ability to control the products produced, especially low boiling aromatics and high surface area char.